Sprayed coating formation device and sprayed coating formation method

ABSTRACT

A sprayed coating formation device for forming a sprayed coating on an inner surface of a bore of a cylinder block is provided. The sprayed coating formation device includes a molten-particle jet portion configured to melt a thermal spray material by an arc discharge generated by applying a current to the thermal spray material. The molten-particle jet portion includes a gas jet portion. The gas jet portion is configured to jet a gas to the thermal spray material that is melted, in a direction toward the inner surface. A heater is configured to heat the gas in advance before jetting.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2015-164655 filed on Aug. 24, 2015 including the specification, drawings and abstract is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a sprayed coating formation device and a sprayed coating formation method, and relates to, for example, a sprayed coating formation device and a sprayed coating formation method each for forming a sprayed coating on an inner surface of a bore of a cylinder block.

2. Description of Related Art

In order to improve an abrasion resistance or the like, a sprayed coating is formed on an inner surface of a bore of a cylinder block in which a piston of an engine is accommodated. Japanese Patent Application Publication No. 2002-030411 (JP 2002-030411 A) discloses a method for forming a sprayed coating on an inner surface of a bore by inserting a plasma spraying device into the bore. In this method, in order to prevent overheating of a base material of a cylinder block, a coolant gas is jetted from a part inserted in the bore so as to keep a temperature of the base material below 200° C. On this account, the plasma spraying device disclosed in JP 2002-030411 A requires a cooling mechanism for the base material separately.

SUMMARY

Here, in a case where a thermal spray material is melted and sprayed on the base material as molten particles, as a time until the molten particles solidify after they are attached to the base material is longer, an adhesion property of a sprayed coating with respect to the base material improves. From this point, it is preferable that a temperature when the molten particles are attached to the base material be high.

However, the bore on which the sprayed coating is formed is generally at an ordinary temperature and a time until the temperature of the molten particles reaches a solidification temperature is short, so the adhesion property of the sprayed coating with respect to the base material decreases.

The present disclosure provides a sprayed coating formation device and a sprayed coating formation method each of which is able to improve an adhesion property of a sprayed coating.

A sprayed coating formation device for forming a sprayed coating on an inner surface of a bore of a cylinder block is provided. The sprayed coating formation device includes a molten-particle jet portion configured to melt a thermal spray material by an arc discharge generated by applying a current to the thermal spray material. The molten-particle jet portion includes a gas jet portion. The gas jet portion is configured to jet a gas to the thermal spray material that is melted, in a direction toward the inner surface. A heater is configured to heat the gas in advance before jetting.

With such a configuration, since a temperature increase of the base material is restrained in the sprayed coating formation device using the arc discharge in comparison with a plasma spraying device. Therefore, it is possible to form a sprayed coating without providing a cooling device for the inner surface of the bore. Further, the temperature of molten particles at the time of being attached to the inner surface of the bore can be increased by heating the gas to be jetted. This makes it possible to lengthen the time until the molten particles solidify after they are attached to the base material. Hereby, it is possible to improve an adhesion property of the sprayed coating.

According to the above mentioned aspect, when the formation of the sprayed coating, the heater may be placed outside the bore of the cylinder block. This makes it possible to provide the heater without making a large change in the molten-particle jet portion.

According to another aspect of the disclosure, a spray coating formation method for forming a sprayed coating on an inner surface of a bore of a cylinder block by use of a sprayed coating formation device is provided. The sprayed coating formation device includes a molten-particle jet portion and a heater. The molten-particle jet portion includes a gas jet portion. The sprayed coating formation method includes: heating a gas in advance before jetting; melting a thermal spray material by the molten-particle jet portion; and jetting the gas to the thermal spray material that is melted, in a direction toward the inner surface. The thermal spray material is melted by an arc discharge generated by applying a current to the thermal spray material.

According to the above mentioned aspect, when the sprayed coating is provided, the molten-particle jet portion may be inserted into the bore of the cylinder block, and the heater may be placed outside the bore of the cylinder block.

According to the present disclosure, it is possible to provide a sprayed coating formation device and a sprayed coating formation method each of which is able to improve an adhesion property of a sprayed coating.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance of exemplary embodiments will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein:

FIG. 1 is a configuration diagram exemplifying a sprayed coating formation device according to an embodiment;

FIG. 2 is a sectional view exemplifying part of a molten-particle jet portion in the sprayed coating formation device according to the embodiment;

FIG. 3 is a process drawing exemplifying a sprayed coating formation method using the sprayed coating formation device according to the embodiment, and steps in a comparative example are shown on an upper side while steps in the present embodiment are shown on a lower side;

FIG. 4 is a view exemplifying a temperature change of molten particles in the sprayed coating formation device according to the embodiment, and a horizontal axis indicates an elapsed time while a vertical axis indicates a temperature of the molten particles; and

FIG. 5 is a graph exemplifying a relationship between a temperature of a jet gas and a temperature of flying molten particles in the sprayed coating formation device according to the embodiment, and a horizontal axis indicates the temperature of the jet gas while a vertical axis indicates the temperature of the flying molten particles in the vicinity of the bore.

DETAILED DESCRIPTION OF EMBODIMENTS

The following describes a best mode for carrying out the present disclosure with reference to the attached drawings. However, the present disclosure is not limited to the following embodiment. Further, the following description and drawings are simplified appropriately for clarification of the description.

First described is a sprayed coating formation device according to the embodiment. The sprayed coating formation device is a device for forming a sprayed coating on an inner surface of a bore of a cylinder block in which a piston of an engine is accommodated. The following first describes a configuration of the sprayed coating formation device.

FIG. 1 is a configuration diagram exemplifying the sprayed coating formation device according to the embodiment. As illustrated in FIG. 1, the sprayed coating formation device 100 includes a molten-particle jet portion 10 and a heater 20. The molten-particle jet portion 10 includes a nozzle 11 and wire rod holders 12. The heater 20 includes gas cylinders 21 and a heater 22.

A shape of the nozzle 11 is tubular. One end of the nozzle 11 is a thin spray port 11 a. A gas pipe 31 is connected to the other end of the nozzle 11 on an opposite side to the spray port 11 a. The nozzle 11 jets, from the spray port 11 a, a gas supplied from the gas pipe 31. The gas thus jetted from the spray port 11 a is called a jet gas 18. Thus, the molten-particle jet portion 10 includes a gas jet portion such as the nozzle 11, for example.

A plurality of wire rod holders 12, e.g., two wire rod holders 12 are provided. The wire rod holder 12 holds a thermal spray material 14. The wire rod holder 12 holds the thermal spray material 14 such that a distal end 14 a of the thermal spray material 14 is placed in front of the spray port 11 a in a gas jetting direction. A gap is formed between respective distal ends 14 a of the thermal spray materials 14. The wire rod holder 12 is configured such that, when the distal end 14 a of the thermal spray material 14 melts to be worn out, the wire rod holder 12 sends out the thermal spray material 14 so that the distal end 14 a of the thermal spray material 14 is always placed in front of the spray port 11 a of the nozzle 11 in the gas jetting direction. The wire rod holder 12 is electrically connected to a direct current power supply via a wiring 41. Hereafter the direct current power supply is referred to as DC. A current is supplied to the wire rod holder 12 from the DC power supply via the wiring 41. The current thus supplied from the DC power supply is supplied to the thermal spray material 14 via the wire rod holder 12. The DC power supply generates an arc discharge by applying the current to the thermal spray material 14.

The gas cylinder 21 in the heater 20 is provided for each gas type. For example, a plurality of gas cylinders 21 is provided. One of the gas cylinders is filled with air, for example. Another one of the gas cylinders is filled with nitrogen (N₂), for example. Further, respective gas pipes 32 are connected to respective gas cylinders 21. The gas pipes 32 thus connected to respective gas cylinders 21 are connected together to be unified into one gas pipe 32, which is connected to the heater 22. The gas pipe 31 and the gas pipes 32 are each provided with an opening/closing valve appropriately.

The heater 22 is configured such that a gas flows inside the heater 22. The gas pipes 32 connected to the gas cylinders 21 are connected to one end of the heater 22. The gas pipe 31 connected to the nozzle 11 is connected to the other end of the heater 22. The gas in the gas cylinder 21 flows inside the heater 22 so as to be supplied to the nozzle 11. For example, a plurality of heat sources for generating far infrared rays is provided inside the heater 22. A gas pipe is placed in the vicinity of the heat sources. The heater 22 hereby heats a gas flowing inside the heater 22.

FIG. 2 is a sectional view exemplifying part of the molten-particle jetting portion in the sprayed coating formation device according to the embodiment. As illustrated in FIG. 2, the molten-particle jet portion 10 is configured such that the gas pipe 31, the thermal spray materials 14, and the nozzle 11 are integrated with each other, for example. The molten-particle jet portion 10 has an axis A extending in a direction where the gas pipe 31 and the thermal spray materials 14 extend. The spray port 11 a of the nozzle 11 faces toward a direction perpendicular to the axis A. The thermal spray material 14 is held such that the distal end 14 a of the thermal spray material 14 is placed in front of the spray port 11 a in the gas jetting direction. The gas pipe 31 extending along the axis A is connected to the other end of the nozzle 11. The spray port 11 a of the nozzle 11 may not face toward the direction perpendicular to the axis A, provided that the jet gas 18 is jetted toward an inner surface of a bore 51.

Next will be described an operation of the sprayed coating formation device 100 according to the embodiment. As illustrated in FIGS. 1 and 2, the operation is described by taking, as an example, a case where a sprayed coating 15 is provided on an inner surface 51 a of a bore 51 of a cylinder block 50. First, the molten-particle jet portion 10 is inserted into the cylinder block 50. Then, the spray port 11 a is directed toward the inner surface 51 a of the bore 51. The heater 20 is placed outside the cylinder block 50.

As such, when the formation of the sprayed coating 15, the molten-particle jet portion 10 is inserted into the bore 51 of the cylinder block 50, and the heater 20 is placed outside the bore 51 of the cylinder block 50. This makes it possible to provide the heater 20 without making a large change in the molten-particle jet portion 10.

Valves of the gas cylinders 21 are opened. The air and the nitrogen (N₂) gas flow through the gas pipes 32, the heater 22, and the gas pipe 31. When the gas passes through the heater 22, the gas becomes a hot gas. Thus, the heater 20 heats a gas to be jetted, in advance before jetting. For example, when a gas at 20° C. in the gas pipe 32 passes through the heater 22, its temperature increases to 300° C. The temperature of the gas before heating and the temperature of the gas after heating are not limited to the above. Optimum temperatures are selected appropriately depending on a type of the gas, a type of the thermal spray material 14, and a place where the sprayed coating 15 is formed. The gas thus heated flows through the gas pipe 31, and is jetted ahead of the spray port 11 a from the spray port 11 a of the nozzle 11 at a high speed.

Meanwhile, the DC power supply applies a direct current between two wire rod holders 12. A voltage is applied between the thermal spray materials 14 held by the wire rod holders 12. When the current is applied to the thermal spray materials 14, an arc discharge 16 is generated between the distal ends 14 a of the thermal spray materials 14. Hereby, the thermal spray materials 14 melt. The gas jet portion of the molten-particle jet portion 10 jets a gas directed toward the inner surface of the bore 51, with respect to the thermal spray materials 14 melted by the arc discharge. The thermal spray materials 14 that are melted are atomized to become molten particles 17. Thus, the molten-particle jet portion 10 jets the molten particles 17 formed from the thermal spray materials 14 thus melted with respect to the inner surface 51 a of the bore 51 together with the jet gas 18.

The molten particles 17 fly with the jet gas 18, and are welded to the inner surface 51 a of the bore 51. Inside the bore 51 of the cylinder block 50, the molten-particle jet portion 10 is moved along a direction of the axis A while being rotated around the axis A as a rotating axis. By moving the molten-particle jet portion 10 as such, the sprayed coating 15 is formed on the inner surface 51 a of the bore 51.

Next will be described a step flow using the sprayed coating formation device 100 according to the embodiment. For example, a step of forming the sprayed coating 15 on the inner surface 51 a of the bore 51 of the cylinder block 50 is described.

FIG. 3 is a process drawing exemplifying a sprayed coating formation method using the sprayed coating formation device according to the embodiment, and steps in a comparative example are shown on an upper side while steps in the present embodiment are shown on a lower side.

First, the comparative example on the upper side is described. In the comparative example, the inner surface 51 a of the bore 51 before thermal spraying is roughened (step S11). This is performed to facilitate adhesion of the sprayed coating 15. Then, a base material of the cylinder block 50 is preheated before thermal spraying (step S12). In the comparative example, the sprayed coating 15 is formed on the inner surface 51 a of the bore 51 of the cylinder block 50 by use of electric arc spraying. Accordingly, differently from plasma spray, in order to improve the adhesion property of the sprayed coating, preheating of the base material of the cylinder block 50 is required. The electric arc spraying is a method to perform thermal spraying by use of an arc discharge.

Then, the electric arc spraying is performed (step S13). Hereby, the sprayed coating 15 is formed on the inner surface 51 a of the bore 51. In the electric arc spraying in the comparative example, the jet gas 18 is not heated. After that, a post-process is performed on the inner surface 51 a of the bore 51 (step S14). That is, a process such as grinding is performed on the sprayed coating 15 formed on the inner surface 51 a. Thus, the sprayed coating 15 in the comparative example is formed.

In the comparative example, the preheating of the cylinder block 50 is performed. In order to improve an adhesion property between the base material and the sprayed coating 15 and an adhesion property of the whole sprayed coating 15 (between the molten particles 17), a technique to preheat the base material of the cylinder block 50 is generally known. The cylinder block 50 is made of aluminum-based or iron-based alloy. Further, a mass of the cylinder block 50 is 15 to 30 kg. Accordingly, a heat capacity of the cylinder block 50 is large. In addition to this, a thermal conductivity of the cylinder block 50 is also high. Therefore, even when a preheating-required part of the bore 51 is preheated, the heat is conducted to the vicinity of the bore 51.

For these reasons, it is necessary to preheat the whole cylinder block 50 to a temperature higher than a given temperature. This accordingly requires facilities such as a preheating furnace, which increases a production cost. Further, due to the influence of a temperature increase of the whole cylinder block 50, the molten particles 17 are attached to parts other than the bore 51 and remain on the parts other than the bore 51. Because of this, masking and removal (high-pressure cleaning or the like) in the post-process are required, which increases the production cost.

In the meantime, as illustrated on the lower side in FIG. 3, in the present embodiment, first, the inner surface 51 a of the bore 51 before thermal spraying is roughened (step S21), which is a similar step to the comparative example. Then, electric arc spraying is performed (step S22). In the present embodiment, the electric arc spraying is performed by use of a gas heated to a high temperature. Hereby, the sprayed coating 15 is formed on the inner surface 51 a of the bore 51. Then, a post-process similar to the comparative example is performed on the bore (step S23). Thus, the sprayed coating 15 of the present embodiment is formed.

In the present embodiment, preheating of the base material of the cylinder block 50 before the thermal spraying as shown in step S12 is not required. Accordingly, facilities such as a furnace necessary for the preheating are not required. Further, it is possible to restrain the molten particles 17 from being attached to parts other than the bore 51 and remaining on the parts other than the bore 51. Further, the step of preheating is omitted, thereby making it possible to shorten the time required for the step. As such, the sprayed coating formation device 100 of the embodiment can reduce the production cost in comparison with the comparative example.

FIG. 4 is a view exemplifying a temperature change of the molten particles in the sprayed coating formation device according to the embodiment, and a horizontal axis indicates an elapsed time while a vertical axis indicates a temperature of the molten particles. A temperature change in the present embodiment using a hot gas is indicated by a broken line (EMBODIMENT). A temperature change in a comparative example in which the preheating of the base material is performed is indicated by a dotted line (WITH PREHEATING). A temperature change in a comparative example in which the preheating of the base material is not performed is indicated by a continuous line (WITHOUT PREHEATING).

As illustrated in FIG. 4, in the present embodiment using the hot gas, the temperature of the flying molten particles 17 decreases over time. However, during the flying, the temperature of the molten particles 17 of the present embodiment is higher than temperatures of the molten particles 17 in the comparative examples. In the present embodiment, a temperature decrease of the flying molten particles 17 is restrained by heating a gas to be jetted. Further, in the present embodiment, the temperature of the molten particles 17 at the time of being attached to the base material of the bore 51 is higher than those of the comparative examples. Further, a time Δt until the molten particles 17 solidify on the base material after the adhesion to the base material of the bore 51 is long to the same extent as the comparative example with preheating.

Meanwhile, in the comparative example with preheating, the temperature of the flying molten particles 17 decreases over time. The temperature of the flying molten particles 17 is lower than that of the present embodiment. This is presumably because the molten particles 17 are cooled off by their peripheral gas during the flying of the molten particles 17. Further, in the comparative example with preheating, the temperature of the molten particles 17 at the time of being attached to the base material is lower than that of the present embodiment. A time until the molten particles 17 solidify after they are attached to the base material is about the same as the present embodiment. Since the preheating is performed on the base material, the time until the solidification is long to the same extent as the present embodiment.

In the comparative example without preheating, the temperature of the flying molten particles 17 decreases over time. The temperature of the flying molten particles 17 is lower than that of the present embodiment. Similarly to the comparative example with preheating, this is presumably because the molten particles 17 are cooled by their peripheral gas during the flying of the molten particles 17. The temperature of the molten particles 17 at the time of being attached to the base material is also lower than that of the present embodiment. A time until the molten particles 17 solidify after they are attached to the base material is shorter than those of the present embodiment and the comparative example with preheating.

It is known that the time (Δt) until the molten particles 17 solidify after they are attached to the base material has a correlation with an adhesion property of the sprayed coating 15. This is presumably because, when the molten particles 17 solidify after they are attached to the base material, a tensile stress is caused in the sprayed coating 15. Further, it is also known that, when the molten particles 17 are suddenly solidified, the tensile stress caused in the sprayed coating 15 becomes higher. The preheating of the base material relaxes a gradient of the temperature decrease after the molten particles 17 are attached to the base material.

The method using the hot jet gas 18 in the present embodiment can restrain the temperature decrease of the flying molten particles 17. This accordingly makes it possible to achieve a higher temperature at the time of adhesion to the base material, as compared with the comparative examples. Hereby, the time until the molten particles 17 solidify can be lengthened. This makes it possible to ease the occurrence of the stress and to improve the adhesion property.

As a method to improve the adhesion property of the sprayed coating, there is laser assisted irradiation by irradiating the sprayed coating 15 with a laser beam. However, in a case where the sprayed coating 15 is formed inside the bore 51 of the cylinder block 50, it is necessary to insert, into the bore 51, a component such as a laser pipe for performing the laser assisted irradiation. Further, it is necessary to take measures for a foreign matter to be attached to a laser irradiation portion. In this regard, in the method of the present embodiment, it is not necessary to newly insert a component such as the laser pipe into the bore 51, and it is not necessary to take measures for a foreign matter to be attached to the laser irradiation portion.

FIG. 5 is a graph exemplifying a relationship between a temperature of the jet gas and a temperature of the flying molten particles in the sprayed coating formation device according to the embodiment, and a horizontal axis indicates the temperature of the jet gas while a vertical axis indicates the temperature of the flying molten particles in the vicinity of the bore.

As illustrated in FIG. 5, by increasing the temperature of the jet gas 18, it is possible to increase the temperature of the flying molten particles 17 in the vicinity of the bore. For example, in a case where the jet gas 18 is not heated by the heater 22, the temperature of the jet gas 18 is 20° C. At this time, the temperature of the flying molten particles 17 around the bore 51 is 2130° C. In the meantime, when the temperature of the jet gas 18 is increased to 100° C. by the heater 22, the temperature of the flying molten particles 17 around the bore 51 is 2180° C. When the temperature of the jet gas 18 is increased to 200° C., the temperature of the molten particles 17 reaches 2240° C., and when the temperature of the jet gas 18 is increased to 300° C., the temperature of the molten particles 17 reaches 2280° C. Accordingly, by increasing the temperature of the jet gas 18 from 20° C. to 300° C., it is possible to increase the temperature of the molten particles 17 by about 150° C.

Note that an early temperature of the molten particles 17 by the arc discharge 16 is 3000° C. A particle diameter of the flying molten particle 17 is 50 μm. A density of the thermal spray material 14 is 7070 kg/m³. A specific heat of the thermal spray material 14 is 460 J/(kg/K).

The following describes effects of the present embodiment. In the sprayed coating formation device 100 according to the present embodiment, the gas to be jetted to the melted thermal spray materials 14 is heated in advance before jetting. This makes it possible to restrain the molten particles 17 from being cooled by their peripheral gas during the flying to the inner surface 51 a of the bore 51. Further, it is possible to increase the temperature of the molten particles when the molten particles 17 are attached to the inner surface 51 a of the bore 51. This makes it possible to lengthen the time until the molten particles 17 solidify after they are attached to the inner surface 51 a. Hereby, an occurrence of the stress in the sprayed coating 15 is restrained, thereby making it possible to improve the adhesion property between the base material of the cylinder block 50 and the sprayed coating 15 and the adhesion property of the whole sprayed coating 15.

Further, the preheating of the base material of the cylinder block 50 before the thermal spraying is not required. Accordingly, facilities such as a furnace are not required. Further, the step of preheating can be shortened. This makes it possible to reduce the production cost. Further, differently from the plasma spray, the electric arc spraying does not overheat the base material. Accordingly, facilities such as a cooling mechanism for the base material are also not required. Furthermore, it is not necessary to insert new equipment into the bore 51, unlike the laser assisted irradiation.

When the formation of the sprayed coating 15, the molten-particle jet portion 10 is inserted into the bore 51 of the cylinder block 50, and the heater 20 is placed outside the bore 51 of the cylinder block 50. This makes it possible to provide the heater 20 without making a large change in the molten-particle jet portion 10.

The embodiment of the sprayed coating formation device according to the present disclosure has been described above, but the present disclosure is not limited to the above configuration, and the above embodiment can be modified without departing from a technical idea of the present disclosure.

For example, the present embodiment deals with a case where the sprayed coating formation device 100 is used to form the sprayed coating 15 inside the bore 51 of the cylinder block 50. However, the sprayed coating formation device 100 may be applied to a case where the sprayed coating 15 is formed in a part other than the inside of the bore 51 of the cylinder block 50. Further, the molten-particle jet portion 10 is configured such that the nozzle 11, the gas pipe 31, and the wire rod holders 12 are integrated with each other, but may be configured such that they are provided separately. 

What is claimed is:
 1. A sprayed coating formation device for forming a sprayed coating on an inner surface of a bore of a cylinder block, the sprayed coating formation device comprising: a molten-particle jet portion configured to melt a thermal spray material by an arc discharge generated by applying a current to the thermal spray material, the molten-particle jet portion including a gas jet portion, the gas jet portion being configured to jet a gas to the thermal spray material that is melted, in a direction toward the inner surface; and a heater configured to heat the gas in advance before jetting.
 2. The sprayed coating formation device according to claim 1, wherein when the sprayed coating is provided, the molten-particle jet portion is inserted into the bore of the cylinder block, and the heater is placed outside the bore of the cylinder block.
 3. A spray coating formation method for forming a sprayed coating on an inner surface of a bore of a cylinder block by use of a sprayed coating formation device, the sprayed coating formation device including a molten-particle jet portion and a heater, the molten-particle jet portion including a gas jet portion, the sprayed coating formation method comprising: heating, by the heater, a gas in advance before jetting; melting a thermal spray material by the molten-particle jet portion, the thermal spray material being melted by an arc discharge generated by applying a current to the thermal spray material; and jetting, by the gas jet portion, the gas to the thermal spray material that is melted, in a direction toward the inner surface.
 4. The spray coating formation method according to claim 3, wherein when the sprayed coating is provided, the molten-particle jet portion is inserted into the bore of the cylinder block, and the heater is placed outside the bore of the cylinder block. 